This invention relates to pneumatic vehicle tires and, more particularly to pneumatic vehicle tires having reinforcing belts in the crown areas thereof.
Pneumatic tires of the "radial ply" and "bias ply" types well known in the art are frequently constructed with a reinforcing belt, commonly referred to as a breaker, interposed between the crown region of the tire carcass and the tire tread for reinforcing the latter. The breaker or belt generally comprises one or more layers or plies of tire cords or cables which are generally inextensible, i.e., made of such materials as metallic wires, glass fiber and textiles such as rayon, nylon, etc. In a mono-ply belt the cords or cables have a relatively low bias angle of 0.degree., i.e., they are oriented substantially parallel to the planes of the beads and to the median equatorial plane or crown centerline of the tire. If the belt is of a multi-ply construction, similar but opposed bias orientation of the cords or cables with respect to the median equatorial plane of the tire are employed in successive plies.
It is known that tires of the type mentioned above, i.e., tires having a tread reinforced by a belt or breaker composed of superposed, mutually crossed, rubberized plies of parallel, essentially inextensible cords or cables, frequently fail because separations occur in the shoulder zones of the tires where the edges of the belt plies are severely flexed as the tire tread moves into and out of contact with the road during each revolution and becomes detached from the surrounding rubber. The centrifugal forces acting on the tire and the heat build-up in the tire also contribute significantly to this problem. Such separations are made even more likely by the fact that the cords or cables in the belt plies, being disposed obliquely to the median equatorial plane of the tire by virture of the plies being cut obliquely with respect to the longitudinal direction of the cords or cables therein, have a natural tendency to spread apart or open in a fan-wise direction at their cut ends. The edges of the belt thus constitute zones or regions where the cut and free ends of the reinforcing elements, i.e., the cords or cables, by friction and by cutting, cause breaks both at their juncture with the carcass plies and the tread rubber of the tire.
One solution which has been proposed to overcome this problem entails the use of a rigid layer of transversely oriented cables positioned radially inward of the breaker layer and a layer of rubber having a Shore A hardness of between 50 and 65 positioned radially inward of the rigid layer. This structure is illustrated in U.S. Pat. No. 3,512,568, issued May 19, 1970 to Kleber-Colombes, a French corporation.
Another solution proposed for overcoming the problem of belt ply edge separation entails the use of reinforcement layers of rubberized, radially oriented, parallel cord material positioned radially outward of the belt edges in the shoulder region of the tire and a layer of rubber having a shore A hardness of 80 disposed about the radially inward and outward marginal portions and the edges of the belt. This structure is illustrated in U.S. Pat. No. 3,598,165 issued Aug. 10, 1971 to the Dunlop Company of England.
It has been found, however, that neither of the above-described structures provide a completely satisfactory solution to the problem of belt ply edge separation. It has been found, in fact, that these structures, to some extent, caused the shoulders of the tires in which they are utilized to become so stiff that driving comfort is reduced.